“Currently there are two dire problems under the spotlight in South Africa; the energy supply crisis and the proliferating creation of waste. Authorities are hard pressed to find effective and sustainable solutions to these quandaries. However, there is a possible solution to satisfy both problems simultaneously,” says Quentin van Coller, Business Development manager at Nyamezela Group.
Nyamezela Group, in conjunction with Matrix Strategic Solutions (a company based in Switzerland), is poised to promote a sustainable and proven “waste-to-energy” (W2E) technology solution in the South African market. Matrix Strategic Solutions specialises in potential development (as opposed to resource utilisation) of sustainability solutions in the fields of energy, environmental and biotech technologies. Matrix Strategic Solutions has a successful track record of international projects of profitable installations, successful sites and unique breakthroughs in their fields of expertise.
“The Consulting Engineers and Energy and Minerals Divisions at Nyamezela Group already have extensive experience in the management of solid waste as well as undertaking projects in the energy/electrical industries,” says Van Coller.
According to Van Coller, the following problems are increasing in magnitude with little or no resolution on the horizon:
• Mounting volumes of waste generation from residential, commercial and industrial sectors.
• Increasing volumes of illegal dumping and the creation of toxic and medical waste.
• Decreasing availability of adequate landfill sites.
• Long term detrimental health effect of the landfill sites – toxic gases, odours and the contamination of ground water.
• Environmental impact and pollution from the incineration by-products in landfills.
• Litter on landscapes.
• Increasing cost of waste disposal.
• Local and global results of carbon emissions pollution.
• Electricity supply not keeping pace with population and industry growth.
• Attempted recycling initiatives not being successful due to budgets, awareness programs, infrastructure and the manpower to be able to fulfil the desired objectives not readily available.
“South Africa has waste, lots of it and the volumes are spiralling out of control,” says Van Coller before explaining that the W2E solution addresses and eliminates all of the above problems with a one-stop sustainable solution that turns garbage into a valuable resource for producing energy as well as a number of ‘clean’ by-products. “This solution fulfils the objectives and criteria publicised in numerous waste management policies and documents generated at local and national level.”
Dumping sites reaching saturation point
“As a developing nation, the primary disposal of all solid waste in South Africa is to dump the waste into designated landfills or onto dump sites. But we are reaching a saturation point in landfills, so where to next?” asks Van Coller. “In developed countries, due to legislation as well as a shortage of ‘waste’ or spare land for landfills, most waste treatment processes are based on incineration where the matter is destroyed with numerous by-products.”
Incineration of waste materials converts the waste into incinerator bottom ash, flue gases, particulates or fly ash and heat, which can in turn be used to generate electric power. The flue gases are cleaned of pollutants before they are dispersed in the atmosphere.
“Fundamentally, the energy of the waste is converted to thermal energy, while the flue gas only carries a small amount of reusable energy. However, the popularity of this technology is waning as the detriments are now far outweighing the benefits,” says Van Coller.
How the W2E solution works
The W2E solution is deployed in a modular fashion by using an optimised module (thermal units) size handling up to 40 000 tons of waste per annum (tpa). For higher quantities of waste processing, an additional 40 000 t.p.a. modules are added in parallel and feeding into a bank of electricity generating units, thus establishing a high degree of redundancy.
“This approach has proven to be more economical than building large thermal blocks, which are difficult to control. Although these modules are all contained in one building, the modularisation allows for a decentralisation strategy, thereby optimising waste removal logistics, urban structure, investment cost and electricity usage in the grid.”
“The W2E process is a pyrolysis process also termed gasification,” says Van Coller.
The W2E process is designed similarly to a naturally occurring gasification system – the volcano. The self-sustaining combustion system (lava) allows the solids to convert to gases on the surface and the surface determines the volume of the process gas. This is time independent.
“As long as organic matter is present, a process gas will be generated. The temperature of this system is high – around 1 500°C, so even steels will melt. Certain rocks will also melt and the enclosed carbon will be released, leaving behind a slag. Generally the gasification process does not generate any ashes or residual particles in the syngas due to the lack of forced incineration. But since certain volatile molecules in their combination form a combustible gas, the syngas is ideal for electricity generation,” says Van Coller.
The W2E process is designed around the gasification process (pyrolysis), whereby it is accepted that the process gas or syngas will contain certain molecular chains which are based on hydrocarbon chains (petroleum products and plastics), which will form dioxins and furans upon cooling and condensation.
“It is for this reason that the process gas will undergo high energy and high temperature cracking by means of a plasma stream, where the remaining molecular chains are cracked into isolated and inactive molecules. This again is a physical process – high kinetic energy is used to crack certain ‘ionic’ molecular links and ‘ionises’ these molecules to become inactive. There is no chemical reaction – it’s physics. This cracking process must be controlled in such a way, that the combustible elements of the gas are not combusted, i.e. the gas is not burnt up. This is only possible when the chemical composition of the gas is known,” says Van Coller.
After the cracking process, the unwanted elements can be simply filtered out on a chemical basis. According to Van Coller, these filtering processes are standard technology and easily controlled. “An example would be how chloride is filtered out by means of calcium carbonate resulting in calcium chloride. There are many companies making use of the gasification process in order to generate electricity and the list of companies installing and those operating plants on the basis of biomass or wood chips, is long. There is nothing unproven in this process. The only drawback is, when using contaminated woods, the filtering system will have to be designed to be able to cope with the toxins,” says van Coller.
About the W2E system
Pyrolysis is the physical decomposition/transition process of condensed organic substances by heating. Decomposition implies the breaking down of present forms of matter, changing the form (from a solid to liquid or from a solid to a gaseous form). Gasification is the transition from a solid to a gaseous form, without the fundamental destruction of matter, which is the case during the incineration process.
Gasification is a process that converts carbonaceous materials, such as coal, petroleum, biofuel, or biomass, into carbon monoxide and hydrogen by reacting with the raw material, such as house waste, or compost at high temperatures with a controlled amount of oxygen and/or steam. The resulting gas mixture is called synthesis gas or syngas and is itself a fuel. Syngas and flue gas are generally of different composition. Gasification is a method for extracting energy from many different types of organic materials. It should be noted, that Linde has a process, by which plastics can be gasified on the basis of steam.
Differences between incineration and W2E gasification:
Incineration • Incineration produces toxic bottom ash, fly ash and slag, which needs to be landfilled.
• Incineration loses significant amounts of thermal energy.
• A minimum of 60% of the system investment is for filtering, denox etc.
• Incineration is an old and obsolete technology.
W2E• W2E produces no toxic by-products.
• No ash residue.
• All slag is vitrified due to the high temperature and this end product (tiny vitreous pebbles) can be used in road construction.
• No reactive or residual toxins for landfilling.
• The process is designed with an energy transformation focus.
• A W2E plant is a modular system of individual process sections supplied by established companies.
• The W2E process is a conservational and green approach to the waste and mess generated by civilisation.
Key performance indicators of the W2E system
Plant capacity: 120 000 t.p.a.
Process capacity: 13.7 t/hr (329 t/day)
Electricity generation: 270 GWh p.a.
Generator capacity nominal: 33 750 kVA
CO2 savings: 338 000 t.p.a.
CO2 certificate value: Approximately 57 500 000 ZAR p.a
Plant capacity: 200 000 t p.a.
Process capacity: 22.8 t/hr (548 t / day)
Electricity generation: 747 GWh p.a.
Generator capacity nominal: 104 460 kVA
CO2 savings: 980 000 t.p.a.
CO2 certificate value: Approximately 160 660 000 ZAR p.a.
